How to Make a Box Chair Cushion

Measure the length and width of the seat pad to determine the size of the cushion. Also determine the depth of the seat pad to calculate the finished cushion’s depth. Cut foam to measure 1/2-inch smaller than the dimensions of the seat pad.

Iron the decorative fabric you want to cover the cushion to remove folds and creases. Cut two identical fabric pieces that measure the cushion’s width by its desired length, plus 1/2 inch to all the edges for seam allowances. Place these cutouts that form the upper and lower covers aside.

Cut two lengths of fabric that measure the cushion length by required depth, plus 1/2-inch to all edges for seam allowances. These two strips or lengths of fabric combined together form the gusset -- the pieces between the upper and lower cushion covers that give it depth.

Sew the edges of the gusset together, 5/8 inch from the edges, forming a loop.

Spread the cutout for the upper cushion cover in front of you. Mark a line that measures 5/8 inch in from the edges around the cutout. Repeat the process on the cutout for the lower cushion cover.

Spread the gusset on a table and align the top cover cutout next to it. Insert pins to join the upper edge of the gusset to the edges of the cover, right sides facing. Ensure the corners of the fabrics match.

Remove the pins as you sew the fabrics together along the 5/8-inch seam line. Repeat the process to sew the lower edge of the gusset to the lower cover cutout. Do not stitch all the way around the lower cutout; leave an 18- to 20-inch opening for the foam.

Slide the foam into the opening, matching its corners to the edges of the cover. Slip stitch the opening closed by hand, using thread that matches the fabric.